1. Field of the Invention
The invention relates to a process for the catalytic dehydrogenation of diols with 3 to 10 carbon atoms on a catalyst containing copper and chromium.
2. Discussion of the Background
When diols are catalytically dehydrogenated the product formed is mainly formed of aldehydes and lactones. These products are used, inter alia, as perfumes, are employed as solvents and, furthermore, find utility as precursors for pharmaceutical products and polymers.
The catalytic dehydrogenation of alcohols or diols on catalysts containing copper and chromium is generally known. The preparation of lactones by dehydrogenation over copper oxide in the liquid phase is described (see Be. Berthon et al., Tetrahedron Letters 22 (41) 4073-6 (1961)). The use of Cu/Cr catalysts with and without added BaO for the dehydrogenation of alcohols is moreover disclosed in industrial brochures, for example of Sudchemie, Mallinckrodt and Harshaw (Engelhard).
JP-A 61/246173 discloses the preparation of .gamma.-butyrolactone by the dehydrogenation of butanediol over Cu/Cr/Mn or Cu/Cr/Zn catalysts. Hydrogen is added to the reaction medium to increase the useful life of the catalyst. According to WO 92/00 973 (U.S. Pat. No. 5,110,954) diols are dehydrogenated in the liquid phase using a finely divided, suspended copper oxide or copper/chromium catalyst. The dehydrogenation can be carried out according to the prior art in the liquid phase over fixed bed catalysts or in suspension as well as in the gas phase over fixed bed catalysts.
The disadvantage of gas-phase dehydrogenation is the relatively fast inactivation of the catalyst. In addition, the selectivity to product is reduced at the relatively high reaction temperatures which are required. Attempts to increase the useful life of the catalyst by adding additional hydrogen by reducing the boiling points of the diols, which are usually high, by dilution with inert gas and thus to increase the selectivity, do indeed lead to slight improvements but, at the same time, adversely affect the economics of the process.
Liquid-phase dehydrogenation suffers from selectivities which are too low and conversions which are too small.